Cellular telephone carriers in the United States and Europe are required by law to be able to locate a given telephone, in the event that telephone calls for emergency services (such as by calling “911” in the United States) are placed. To this end, cellular telephones typically employ Assisted Global Positioning System (aGPS) transceivers, which is an enhanced version of the GPS systems which calculate the position of a device using data gathered from satellites orbiting the Earth.
The output from aGPS and GPS is a set of location coordinates; i.e., a pair of numbers identifying the approximate longitude and latitude of the device. Potentially, the information related to the location of a cellular telephone or other GPS-enabled device could be used for purposes other than providing emergency services. For example, the device could alert the user when a particular store, or any person on a predetermined “buddy” list, is within a predetermined distance. In fact, an entire industry is presently developing, for the purpose of providing Location Based Services (LBS) such as these. This industry is projected to grow rapidly.
The above-described emerging industry must deal with concerns regarding privacy of the device users. Many persons are understandably concerned about the existence of detailed records of the movement of their cellular telephones (and, thus, the persons themselves). For this reason, many cellular telephone carriers have adopted detailed policies to address these privacy concerns. For example, the privacy policy of Verizon Wireless® is to not retain this personally identifiable position data any longer than necessary for technical service purposes.
However, as more and more people carry cellular telephones (and similar devices) with them, information about the movements of these devices can be a useful proxy for the movements of people generally. Thus, for example, a statistically valid sample of the tracks of a small percentage of the cellular telephones in a metropolitan area could provide a precise, graphic illustration of the flow of humanity during rush hour.
It would be desirable to be able to provide a tracking system, for demographic and other purposes, which could follow the movements of cellular or other portable devices, but which will not compromise the privacy of the users of these devices. For example, a complete log of a cellular telephone's movements would show the location of the owner's home. Such information would compromise the owner's identity and privacy. However, if the location information in the log were sufficiently vague about the location of the device when it leaves a public space (e.g., a train station or street) and moves into a residential neighborhood or office, then privacy could be protected. Thus, a method of providing location-based information without compromising a user's privacy solving the aforementioned problems is desired.